As one of Britain’s leading political journalists, with a reputation for asking tough questions, and as a woman, Ms. Kuenssberg has long been the target of vitriolic abuse and threats of violence. But the sight of her being shadowed by a guard, and the realization that her employers must now deem those threats credible enough to warrant giving her protection, has shocked some members of the British commentariat.

“It is so profoundly depressing,” said Jenni Russell, a prominent columnist and former BBC editor who also attended the conference. “The graphic level of threats to women is quite extraordinary and it’s one of the worst things to have happened in recent British public life.”

Multiple journalists have seen Ms. Kuenssberg with a guard this week, although she and the BBC both declined to comment, or to confirm or deny the news. Others spoke of how her experience was part of an international trend in which public discourse has become more venomous, and trust in mainstream journalists has eroded.

Her case has some parallels with the intimidation of journalists at rallies during President Trump’s election campaign, in particular of Katy Tur, an NBC correspondent who was protected by a Secret Service agent as she left a rally in 2015 at which the future president had singled her out for criticism.

But Ms. Kuenssberg’s treatment has a specifically British context. Unlike in America, the threats of violence against her and other journalists have not followed rhetorical attacks by leading politicians — Mr. Corbyn himself condemned online abuse in a major speech on Wednesday — but have instead come from members of the public.

“We are worlds apart from the kind of systematic abuse of the media that Trump engages in,” said Robert Peston, the political editor of ITV, one of the BBC’s main commercial rivals. “There’s not a single occasion that I can think of where Corbyn has said anything critical of Laura Kuenssberg, so it’s very different to the Trump situation in that sense.”

In the latest salvo, The Canary claimed on Wednesday that Ms. Kuenssberg had agreed to speak at an event associated with the governing Conservative Party — an allegation the BBC quickly said was false.

This is a new phenomenon, says Martin Moore, who heads the Center for the Study of Media, Communication and Power at King’s College London.

In recent decades, the BBC has been a frequent punching bag for right-wing politicians and commentators, who have portrayed it as a bastion of closet liberals. But Dr. Moore’s research into criticism of the BBC during the recent general election found that much “came from the left as well,” he said.

“The BBC was being attacked from both right and left — and that is a difference from the past,” Dr. Moore added.

This shift is related to Mr. Corbyn’s political ideology, which is more left-wing than that of his predecessors in the Labour Party leadership.

His stances have widespread support among party members, but have brought him frequent criticism and disdain from Labour lawmakers, many of whom hold more centrist views. Mr. Corbyn’s supporters argue that this treatment has been mimicked by BBC reporters like Ms. Kuenssberg, much as Bernie Sanders’s backers felt the American media establishment gave him a harder time than his opponent in the 2016 Democratic primary, Hillary Clinton.

“I think that has left people thinking that the political culture at the BBC is one that is not sympathetic to new and emerging forms of politics and in fact is committed to sabotaging them,” said Ash Sarkar, a senior editor at Novara Media, one of the new crop of online left-wing outlets.

But it is important to differentiate between this more measured critique of Ms. Kuenssberg’s work, and the vitriol she receives from abusive trolls, Ms. Sarkar said.

“There is a distinction between asking: ‘Is Laura Kuenssberg a good journalist?’, which to me is very much up for debate, and: ‘Does Laura Kuenssberg deserve abuse?’, which for me is a straight-up ‘no,’ ” said Ms. Sarkar, who also receives regular online abuse. “I don’t think there is any journalism that someone could put out that could justify it.”

Commentators from all sides also cautioned against framing Ms. Kuenssberg’s treatment as solely a problem for the left.

“This is true of both left and right,” Mr. Peston said. “Labour women face appalling abuse and Tory women face appalling abuse. It’s quite difficult to say that this is to do with Corbyn, or the far left. This is to do with an era in which there is more extremism on both sides.”

Nor, Ms. Russell said, is it a problem that affects men and women equally. Men might get called names, she said. “Women get told, ‘I’m going to rape you.’ ”